GRAPP 2014 Abstracts

Area 1 - Geometry and Modeling
Full Papers Short Papers
Area 2 - Rendering
Full Papers Short Papers
Area 3 - Animation and Simulation
Full Papers Short Papers
Area 4 - Interactive Environments
Full Papers Short Papers
Area 5 - Social Agents in Computer Graphics
Short Papers

Area 1 - Geometry and Modeling

Full Papers
Paper Nr: 4
Title:

Shape Transformation of Multidimensional Density Functions using Distribution Interpolation of the Radon Transforms
Authors:

Márton József Tóth and Balázs Csébfavi
Abstract: In this paper, we extend 1D distribution interpolation to 2D and 3D by using the Radon transform. Our algorithm is fundamentally different from previous shape transformation techniques, since it considers the objects to be interpolated as density distributions rather than level sets of Implicit Functions (IF). First, we perform distribution interpolation on the precalculated Radon transforms of two different density functions, and then an intermediate density function is obtained by an inverse Radon transform. This approach guarantees a smooth transition along all the directions the Radon transform is calculated for. Unlike the IF methods, our technique is able to interpolate between features that do not even overlap and it does not require a one dimension higher object representation. We will demonstrate that these advantageous properties can be well exploited for 3D modeling and metamorphosis.
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Paper Nr: 8
Title:

3D Graph Reconstruction from 2D Graphs Projections and Univariate Positional Traces in 3-Space - With Application to 3D Reconstruction of Road’s Interchanges
Authors:

Nir Hershko and Gershon Elber
Abstract: In this work, we consider a reconstruction problem of a 3D graph, based on its 2D projected model and imprecise 3D positional traces along it, and propose a general method to achieve this reconstruction. Then, we examine a specific application of this problem—3D reconstruction of road’s interchanges from 2D maps and GPS traces. We demonstrate the algorithm and show that the implementation of this method yields a robust and accurate solution compared to real ground truth data.
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Paper Nr: 44
Title:

Floor Plan Generation and Room Labeling of Indoor Environments from Laser Range Data
Authors:

Eric Turner and Avideh Zakhor
Abstract: Automatic generation of building floor plans is useful in many emerging applications, including indoor navigation, augmented and virtual reality, as well as building energy simulation software. These applications require watertight models with limited complexity. In this paper, we present an approach that produces 2.5D extruded watertight models of building interiors from either 2D particle filter grid maps or full 3D point-clouds captured by mobile mapping systems. Our approach is to triangulate a 2D sampling of wall positions and separate these triangles into interior and exterior sets. We partition the interior volume of the building model by rooms, then simplify the model to reduce noise. Such labels are useful for building energy simulations involving thermal models, as well as for ensuring geometric accuracy of the resulting 3D model. We experimentally verify the performance of our proposed approach on a wide variety of buildings. Our approach is efficient enough to be used in real-time in conjunction with Simultaneous Localization and Mapping (SLAM) applications.
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Paper Nr: 46
Title:

A Practical and Robust Method to Compute the Boundary of Three-dimensional Axis-aligned Boxes
Authors:

Daniel López Monterde, Jonàs Martínez, Marc Vigo and Núria Pla
Abstract: The union of axis-aligned boxes results in a constrained structure that is advantageous for solving certain geometrical problems. A widely used scheme for solid modelling systems is the boundary representation (Brep). We present a method to obtain the B-rep of a union of axis-aligned boxes. Our method computes all boundary vertices, and additional information for each vertex that allows us to apply already existing methods to extract the B-rep. It is based on dividing the three-dimensional problem into two-dimensional boundary computations and combining their results. The method can deal with all geometrical degeneracies that may arise. Experimental results prove that our approach outperforms existing general methods, both in efficiency and robustness.
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Paper Nr: 47
Title:

Non-rigid Registration for Deformable Objects
Authors:

Van-Toan Cao, Van Tung Nguyen, Trung-Thien Tran, Sarah Ali and Denis Laurendeau
Abstract: We present an efficient algorithm for non-rigid registration of two partially overlapping 3D surfaces in which a target surface is a deformed instance of a source surface. The algorithm is implemented in two main phases. In the first phase, the robust algorithm that is used is based on a probability density estimation to find reliable correspondences between the two surfaces. Then, in the second phase, a deformation algorithm is applied for non-rigid registration where the displacement of each point is described by an affine transformation in relation with other points of the same surface and its corresponding point on the other surface. Combined with initial correspondences in the first phase, an effective strategy for optimization of a cost function is carried out to align the two surfaces without using any assumption and user-intervention on the algorithm. We test the robustness of our method by efficiently aligning pairs of surfaces of realistic scan data of human body models.
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Paper Nr: 76
Title:

A Novel Ray-shooting Method to Render Night Urban Scenes - A Method based on Polar Diagrams
Authors:

M. D. Robles-Ortega, J. R. Jiménez and L. Ortega
Abstract: Illumination and shadows are essential to obtain realistic virtual environments. Nevertheless, large scenes like urban cities demand a huge amount of geometry that must somehow be structured or reduced in order to be manageable. In this paper we propose a novel real-time method to determine the shadowed and illuminated areas in large scenes, specially suitable for urban environments. Our approach uses the polar diagram as a tessellation plane, and a ray-casting process to obtain the visible areas. This solution derives the exact illuminated area with a high performance. Moreover, our approach is also used to determine the visible portion of the scene from a pedestrian viewpoint. As a result, we only have to render the visible part of the scene, which is considerably lower than the global scene.
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Paper Nr: 77
Title:

Geodesic Mesh Processing with Edge-Front based Data Structures
Authors:

Hendrik Annuth and Christian-A. Bohn
Abstract: In this paper a novel mesh processing data structure is presented which is efficient in runtime and has an exceptionally low memory consumption. The data structure is extremely versatile and allows investigating various mesh properties without requiring any pre-processing steps such as triangle subdivision or remeshing. The data structure uses an edge-front — a sealed path of mesh edges — whose expansion can by altered to account for individually problem cases. A basic implementation of this data structure — the Minimal Edge Front (MEF) — has already been successfully used to investigate and resolve inconsistently oriented surface regions in a surface reconstruction approach based on an iterative refinement strategy. The MEF is explained in detail and it is augmented to approximate geodesic distances. Due to the used working principal geodesic surface aspects can be analyzed independently of the mesh triangulation and the processing is limited to the investigated area. The edge-front allows to deal with open surfaces and to use points as well as lines as a starting point. The results of the process will be experimentally shown and discussed.
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Short Papers
Paper Nr: 19
Title:

Low-Discrepancy Distribution of Points on Arbitrary Polygonal 3D-surfaces
Authors:

Alena Bulyha, Wolfgang Herzner, Markus Murschitz and Oliver Zendel
Abstract: This paper presents a technique for automatic distribution of points on 3D-surfaces that are defined as meshes of polygons (usually triangles) such that the distribution has a low discrepancy. The work is motivated by the quest for representing arbitrary 3D-objects by a minimal number of surface points such that different views and arbitrary occlusions of objects can be effectively distinguished by simply using the visible surface points. The approach exploits low-discrepancy sequences on the unit square such as those proposed by Hammersley or Halton.
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Paper Nr: 30
Title:

Efficient Registration of Multiple Range Images for Fully Automatic 3D Modeling
Authors:

Yulan Guo, Jianwei Wan, Jun Zhang, Ke Xu and Min Lu
Abstract: Multi-view range image registration is a significant and challenging problem for 3D modeling. This paper presents a reference shape based multi-view range image registration algorithm. First, a set of Rotational Projection Statistics (RoPS) features are extracted from the input range images. Next, the reference shape is initialized by selecting a range image from the input. The reference shape is then iteratively updated by registering itself with the remaining range images. The registration between the reference shape and any range image is completed by RoPS feature matching. Finally, all input range images are registered according to their corresponding reference shapes. A number of experiments were performed to test the performance of our algorithm. The experimental results show that the reference shape based algorithm can perform multi-view registration on a mixed set of unordered range images corresponding to several different objects. It is also very accurate and efficient. It outperformed the state-of-the-arts including the spanning tree based and connected graph based algorithms.
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Paper Nr: 39
Title:

Automatic Method for Sharp Feature Extraction from 3D Data of Man-made Objects
Authors:

Trung-Thien Tran, Van-Toan Cao, Van Tung Nguyen, Sarah Ali and Denis Laurendeau
Abstract: A novel algorithm is proposed for extracting sharp features automatically from scanned 3D data of man-made CAD-like objects. The input of our method consists of a mesh or an unstructured point cloud that is captured on the object surface. First, the vector between a given point and the centroid of its neighborhood at a given scale is projected on the normal vector and called the 'projected distance' at this point. This projected distance is calculated for every data point. In a second stage, Otsu's method is applied to the histogram of the projected distances in order to select the optimal threshold value, which is used to detect potential sharp features at a single scale. These two stages are applied iteratively with the other incremental scales. Finally, points recorded as potential features at every scale are marked as valid sharp features. The method has many advantages over existing methods such as intrinsic simplicity, automatic selection of threshold value, accurate and robust detection of sharp features on various objects. To demonstrate the robustness of the method, it is applied on both synthetic and real 3D data of point clouds and meshes with different noise levels.
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Paper Nr: 54
Title:

Automatic Generation of Structural Building Descriptions from 3D Point Cloud Scans
Authors:

Sebastian Ochmann, Richard Vock, Raoul Wessel, Martin Tamke and Reinhard Klein
Abstract: We present a new method for automatic semantic structuring of 3D point clouds representing buildings. In contrast to existing approaches which either target the outside appearance like the facade structure or rather low-level geometric structures, we focus on the building’s interior using indoor scans to derive high-level architectural entities like rooms and doors. Starting with a registered 3D point cloud, we probabilistically model the affiliation of each measured point to a certain room in the building. We solve the resulting clustering problem using an iterative algorithm that relies on the estimated visibilities between any two locations within the point cloud. With the segmentation into rooms at hand, we subsequently determine the locations and extents of doors between adjacent rooms. In our experiments, we demonstrate the feasibility of our method by applying it to synthetic as well as to real-world data.
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Paper Nr: 59
Title:

3D-NCuts: Adapting Normalized Cuts to 3D Triangulated Surface Segmentation
Authors:

Zahra Toony, Denis Laurendeau, Philippe Giguère and Christian Gagné
Abstract: Being able to automatically segment 3D models into meaningful parts is an important goal in 3D shape processing. In this paper, we are proposing a fast and easy-to-implement 3D segmentation approach, which is based on spectral clustering. For this purpose, we define an improved formulation of the similarity matrix which allows our algorithm to segment both free-form and CAD (Computer Aided Design) 3D models. In 3D space, different shapes, such as planes and cylinders, have different surface normal distributions. We defined the similarity of vertices based on their normals which can segment a 3D model into its geometric features. Results show the effectiveness and robustness of our method in segmenting a wide range of 3D models. Even in the case of complex models, our method results in meaningful segmentations. We tested our segmentation approach on real data segmentation, in the presence of noise and also in comparison with other methods which provided good results in all cases.
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Paper Nr: 69
Title:

Surface Reconstruction of Ancient Water Storage Systems - An Approach for Sparse 3D Sonar Scans and Fused Stereo Images
Authors:

Erik A. Nelson, Ian T. Dunn, Jeffrey Forrester, Timothy Gambin, Christopher M. Clark and Zoë Wood
Abstract: This work presents a process pipeline that addresses the problem of reconstructing surfaces of underwater structures from stereo images and sonar scans collected with a micro-ROV on the islands of Malta and Gozo. Using a limited sensor load, sonar and small GoPro Hero2 cameras, the micro-ROV is able to explore water systems and gather data. As a preprocess to the reconstruction pipeline, a 3D evidence grid is created by mosaicing horizontal and vertical sonar scans. A volumetric representation is then constructed using a level set method. Fine-scale details from the scene are captured in stereo cameras, and are transformed into point clouds and projected into the volume. A raycasting technique is used to trim the volume in accordance with the projected point clouds, thus reintroducing fine details to the rough sonar-generated model. The resulting volume is surfaced, yielding a final mesh which can be viewed and interacted with for archaeological and educational purposes. Initial results from both steps of the reconstruction pipeline are presented and discussed.
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Paper Nr: 81
Title:

Visualization of 3D Cluster Results for Medical Tomographic Image Data
Authors:

Sylvia Glaßer, Kai Lawonn and Bernhard Preim
Abstract: We present an approach for the 3D visualization of clustered tomographic image data using the example of breast perfusion image data. Our visualization provides fast visual access to the amount of clusters, cluster size, presence and amount of outliers, and the spatial extent as well as the spatial orientation of the clusters. The spatial perception of a cluster’s elements is improved with a connection via geometric primitives and appropriate shading styles and color mapping. Our technique can be easily adapted to any cluster result arising from medical tomographic image data.
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Paper Nr: 25
Title:

A Shooting Simulator from Boats
Authors:

Pablo Figueroa, Carlos Francisco Rodriguez, Jose Tiberio Hernandez, Juan Camilo Blanco, Raul Oses and Luis Ballesteros
Abstract: We present a simulator for militar fluvial boats, in which we concentrate in the task of shooting. Shooting from a boat is particularly challenging, due to rapid movements, river conditions, and special considerations that should be taken into account for a shooters security. We present a hardware platform that simulates boat movements under different scenarios. On top of such platform, a user is able to freely move around, aim a target, and shoot by using a handle that holds a display and replicates a large gun. Our system can also report metrics related to a users performance. This paper presents the main hardware and software components, the main tasks we would like to address in our simulator, the information in users reports, and some preliminary tests of the implemented functionality.
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Paper Nr: 33
Title:

Deformation Method for 3D Identikit Creation
Authors:

Petr Martínek and Ivana Kolingerová
Abstract: An identikit is a model of a head created for a purpose of identification. Nowadays, the police use mostly 2D portrait identification, which is simple but has limited possibilities. Therefore, 3D head models have started to be used as identikits. In this paper, we propose small improvements of Free-Form Shape Deformation (FFSD) for 3D identikits creation, which allow modeling new shapes and keeping important details. With these improvements the FFSD method is able to create various and realistic deformations of a human head model which are necessary to make and identikit is a bit quicker. The improved method has been implemented and used in software prepared for the police.
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Paper Nr: 55
Title:

Extending Space Colonization Tree Modeling for Artistic Control and Environmental Interactions
Authors:

Owen Patrick, Manjeet Rege and Reynold Bailey
Abstract: There are a growing number of modeling techniques and algorithms for creating and modifying tree structures, both quickly and realistically. Many of these tools are part of larger software packages used for architecture or landscaping designs. In these tools the tree models are static and come from a library selection. In other areas, such as 3D modeling and design in film and animation, the tree creation tools are more open for artistic creativity and freedom of control. Much research has also been done on growing trees that are sensitive to some environment. That is, growing tree models where genus type, and natural and artificial environment factors are taken into heavy consideration. In this paper, we present an approach that facilitates user creativity while still providing a realistic response to environment factors. Our system adapts the Space Colonization Tree Modeling approach to allow for continued branch addition as well as environmental interaction. Feedback from experienced modelers who participated in a user study revealed that our approach generated the tree skeleton structures they intended and also provided realistic interaction with the environment.
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Paper Nr: 58
Title:

Real-Time 3D Visualization of Accurate Specular Reflections in Curved Mirrors - A GPU Implementation
Authors:

André Lages Miguel, Ana Catarina Nogueira and Nuno Gonçalves
Abstract: This paper presents a vertex-based solution for rendering real-time accurate reflections in quadric mirrors in dynamic scenes using CUDA and OpenGL. Our method, based on forward projection, exploits the global information of the vertices and textures as they are computed from its original positions, to their reflections points in the mirror, and finally, to the eye. This solution does not suffer from parallax or visibility issues, neither does it needs to deal with ray intersection. As viewers navigate through the scene, the reflection points are instantly recalculated, depending on the position of the camera. Thus, given a 3D scene, this method gathers all vertex, light, and texture information and computes them at every instance, finding the reflection points and rendering the reflections on the mirror surface. We also demonstrate the accuracy and performance of our method by rendering two sample scenes.
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Paper Nr: 60
Title:

Shader-based Automatic Camera Layout Optimization for Mobile Robots using Genetic Algorithm
Authors:

Shuiying Wang and Raúl Rojas
Abstract: Given a mobile robot and a certain number of cameras, this paper addresses the problem of finding locations and orientations of the cameras relative to the robot such that an optimality criteria is maximized. The optimality criteria designed in this paper emphasizes the trade-off between the coverage of area of interest around the robot by the cameras subject to occlusion constraints and the proximity of cameras to the robot structure. Real coded genetic algorithm is employed to search for such optimal layout and the optimality criteria serves as the fitness function. The computation intensive parts, namely the coverage and proximity analysis, are adapted to such a form that GPU with programmable shader can be accommodated to accelerate them. A graphical user interface tool is constructed to allow observation and checks during the optimization process. Promising results are displayed in an experiment concerning a truck with seven cameras. The optimization framework outlined in this paper can also be extended to optimize layout of scanning sensors like LiDAR and Radar mounted on arbitrary structures.
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Area 2 - Rendering

Full Papers
Paper Nr: 28
Title:

Variable Penumbra Soft Shadows for Mobile Devices
Authors:

Alun Evans, Javi Agenjo and Josep Blat
Abstract: In many applications of 3D graphics, shadows increase the believability and perceived quality of a scene. With the increase in power of workstation hardware, high-quality soft shadowing has become relatively common in many 3D desktop applications. In parallel, recent years have seen an increase in the availability and use of mobile and tablet based devices. The popularity of such devices is driving an increase in graphics intensive applications targeting the hardware, many of which will naturally require the use of shadowing algorithms. Yet the different architecture of graphics hardware of mobile devices restricts the implementation of many graphics algorithms, particularly those that require multiple references to a texture, such as common shadowing techniques. In this paper, we discuss effective shadowing on mobile devices. We show that even small-kernel Percentage Closer Filtering (PCF) soft shadows provide unacceptable framerates on mobile GPUs, but also how mip-chain dilation of the edges of a shadow map allows improvement performance to acceptable levels. Finally, we extend this technique by quantizing the strength of the detected edge to implement variable penumbra shadowing based on occluder distance.
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Paper Nr: 51
Title:

CoSMo: Intent-based Composition of Shader Modules
Authors:

Georg Haaser, Harald Steinlechner, Michael May, Michael Schwärzler, Stefan Maierhofer and Robert Tobler
Abstract: We propose a novel shader programming model which operates on intent-oriented shader modules instead of specific programs for dedicated GPU rasterization pipeline stages. In constrast to existing pipeline shader frameworks, our system exposes a radically simplified pipeline, which we purposefully aligned with our basic intuition of shaders as per-primitive and per-pixel operations and compositions thereof. This simplicity lends itself to structure modules purely based on their intent, instead of dealing with structure enforced by specific versions of graphics APIs. Consequently, this offers great flexibility when it comes to reusing and combining modules with completely different semantics, or when targeting different graphics APIs. The simplicity and uniformity of our system also motivates automatic parameterization and simplification of shader programs as well as interesting interactive shader development and management techniques.
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Paper Nr: 56
Title:

Refresh Rate Modulation for Perceptually Optimized Computer Graphics
Authors:

Jeffrey Smith, Thomas Booth and Reynold Bailey
Abstract: The application of human visual perception models to remove imperceptible components in a graphics system, has been proven effective in achieving significant computational speedup. Previous implementations of such techniques have focused on spatial level of detail reduction, which typically results in noticeable degradation of image quality. We introduce Refresh Rate Modulation (RRM), a novel perceptual optimization technique that produces better performance enhancement while more effectively preserving image quality and resolving static scene elements in full detail. In order to demonstrate the effectiveness of this technique, we have developed a graphics framework that interfaces with eye tracking hardware to take advantage of user fixation data in real-time. Central to the framework is a high-performance GPGPU ray-tracing engine. RRM reduces the frequency with which pixels outside of the foveal region are updated by the ray-tracer. A persistent pixel buffer is maintained such that peripheral data from previous frames provides context for the foveal image in the current frame. Applying the RRM technique to the ray-tracing engine results in a speedup of 3.2 (260 fps vs. 82 fps at 1080p) for the classic Whitted scene without secondary rays and a speedup of 6.3 (119 fps vs. 19 fps at 1080p) with them. We also observe a speedup of 2.8 (138 fps vs. 49 fps at 1080p) for a high-polygon scene that depicts the Stanford Bunny. A user study indicates that RRM achieves these results with minimal impact to perceived image quality. We also investigate the performance benefits of increasing physics engine error tolerance for bounding volume hierarchy based collision detection when the scene elements involved are in the user’s periphery. For a scene with a static high-polygon model and 50 moving spheres, a speedup of 1.8 was observed for physics calculations.
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Paper Nr: 73
Title:

Efficient Multi-kernel Ray Tracing for GPUs
Authors:

Thomas Schiffer and Dieter W. Fellner
Abstract: Images with high visual quality are often generated by a ray tracing algorithm. Despite its conceptual simplicity, designing an efficient mapping of ray tracing computations to massively parallel hardware architectures is a challenging task.In this paper we investigate the performance of state-of-the-art ray traversal algorithms for bounding volume hierarchies on GPUs and discuss their potentials and limitations. Based on this analysis, a novel ray traversal scheme called batch tracing is proposed. It decomposes the task into multiple kernels, each of which is designed for efficient parallel execution. Our algorithm achieves comparable performance to currently prevailing approaches and represents a promising avenue for future research.
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Paper Nr: 75
Title:

Exploiting Material Properties to Select a Suitable Wavelet Basis for Efficient Rendering
Authors:

Jeroen Put, Nick Michiels and Philippe Bekaert
Abstract: Nearly-orthogonal spherical wavelet bases can be used to perform rendering at higher quality and with significantly less coefficients for certain spherical functions, e.g. BRDF data. This basis avoids parameterisation artifacts from previous 2D methods, while at the same time retaining high-frequency details in the lighting. This paper demonstrates the efficiency of this representation for rendering purposes. Regular 2D Haar wavelets can still occasionally perform better, however. This is due to their property of being fully orthogonal. An important novelty of this paper lies in the introduction of a technique to select an appropriate wavelet basis on-the-fly, by utilising prior knowledge of materials in the scene. To show the influence of different bases on rendering quality, we perform a comparison of their parameterisation error and the compression performance.
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Paper Nr: 84
Title:

Topological Space Partition for Fast Ray Tracing in Architectural Models
Authors:

Maxime Maria, Sébastien Horna and Lilian Aveneau
Abstract: Fast ray-tracing requires an efficient acceleration structure. For architectural environment, the most famous is the cells-and-portals one. Many previous works attempt to automatically construct a good cells-and-portals. We propose a new acceleration structure which extends the classical cells-and-portals. It is automatically extracted from the topological model of a given building. It contains a low number of large volumes, all of them linked into a graph model. The scan of our structure is particularly simple and rapid, using all the topological information available from the topological model. The scan can be done for a single ray, or a wide ray packet. We show in this paper that our structure allows an interactive rendering even for large building models, with direct lighting from some thousands of point lights.
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Short Papers
Paper Nr: 5
Title:

Performance Analysis for GPU-based Ray-triangle Algorithms
Authors:

Juan J. Jiménez, Carlos J. Ogáyar, José M. Noguera and Félix Paulano
Abstract: Several algorithms have been proposed during the past years to solve the ray-triangle intersection test. In this paper we collect the most prominent solutions and describe how to parallelize them on modern programmable graphics processing units (GPUs) by means of NVIDIA CUDA. This paper also provides a comprehensive performance analysis based on several optional features and optimizations (such as back-face culling and the use of pre-computed values) that allowed us to determine the influence of each factor on the performance. Finally, we analyze the architecture of the GPU and its impact on the parallel implementation of each method, as well as the approach used to achieve a high-performance fine-grained parallel computation on the ray-triangle test.
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Paper Nr: 10
Title:

User-guided Modulation of Rendering Techniques for Detail Inspection
Authors:

Ankit Sharma and Subodh Kumar
Abstract: Understanding intricate details of carved models, for example ones prevalent in cultural heritage applications, is often difficult from renderings using traditional illumination models. A number of illustrative rendering techniques are known, but each works well only for some models. We present a rendering system that combines these techniques in an attempt to make the visualization more comprehensible given any context. In particular, our system learns user's visual preferences using exemplars from a domain and applies an appropriate combination of the basis techniques to new meshes from that domain. Given a polygonal mesh, the system applies different rendering techniques to different parts based on local features in order to enhance the overall appearance.
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Paper Nr: 49
Title:

Free Adaptive Tessellation Strategy of Bézier Surfaces
Authors:

Raquel Concheiro, Margarita Amor, Montserrat Bóo and Emilio J. Padrón
Abstract: Rendering of B\'ezier surfaces is currently performed by tessellating the model on the GPU and rendering the highly detailed triangle mesh. Whereas non-adaptive strategies apply the same tessellation pattern to the whole surface resulting in a uniform tessellation of the patch, adaptive approaches make it possible to reduce the number of triangles generated without a loss of quality. However, the most usual approaches to adaptive tessellation have little flexibility and do redundant computations and memory accesses, as each sample is independently evaluated in the Domain Shader of the DirectX11 pipeline. In this paper an adaptive tessellation technique based on the exploitation of the spatial coherence (ESC) data within each surface is presented. The GPU implementation of this technique is simple and efficient and, as consequence, the tessellation of complex models can be performed in real-time. The analysis of the GPU performance and limitations for different adaptive degree of the tessellation performed suggest innovations in future graphics card generations for supporting a larger degree of adaptivity without a penalty.
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Paper Nr: 82
Title:

Clutter Reduction in Rendering of Particle (Atom) Trajectories with Adaptive Position Merging
Authors:

Bidur Bohara and Bijaya B. Karki
Abstract: Visualization of position-time series data from molecular dynamics simulations of a material has to render atomic trajectories, and relevant structural and dynamical information. Clutter/occlusion associated with overlapping trajectories becomes serious even for moderate data sizes. We present an adaptive hierarchical scheme for merging multiple positions along trajectories to significantly reduce the number of points/line segments used for rendering. Our approach finds positions lying within a space window (cut-off distance) from a reference position and merges them into a single position. The window is then moved in time order with merging performed at each successive location. All original positions are thus processed to a reduced number of new (merged) positions, which are further merged with the same or a different cut-off to obtain even fewer positions. This hierarchical merging may continue several levels deep. Moreover, merging can be performed subject to constraint of information, which is displayed (color-coded) along individual trajectories. Both the trajectory geometry and underlying atomic structure become increasingly visible after merging so the nature and extent of atomic arrangements and movements can be better assessed.
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Area 3 - Animation and Simulation

Full Papers
Paper Nr: 26
Title:

Feature Extraction for Human Motion Indexing of Acted Dance Performances
Authors:

Andreas Aristidou and Yiorgos Chrysanthou
Abstract: There has been an increasing use of pre-recorded motion capture data for animating virtual characters and synthesising different actions; it is although a necessity to establish a resultful method for indexing, classifying and retrieving motion. In this paper, we propose a method that can automatically extract motion qualities from dance performances, in terms of Laban Movement Analysis (LMA), for motion analysis and indexing purposes. The main objectives of this study is to analyse the motion information of different dance performances, using the LMA components, and extract those features that are indicative of certain emotions or actions. LMA encodes motions using four components, Body, Effort, Shape and Space, which represent a wide array of structural, geometric, and dynamic features of human motion. A deeper analysis of how these features change on different movements is presented, investigating the correlations between the performers' acting emotional state and its characteristics, thus indicating the importance and the effect of each feature for the classification of the motion. Understanding the quality of the movement helps to apprehend the intentions of the performer, providing a representative search space for indexing motions.
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Paper Nr: 38
Title:

MORPHO-Map - A New Way to Model Animation of Topological Transformations
Authors:

Annie Luciani, Ali Allaoui, Nicolas Castagné, Emmanuelle Darles, Xavier Skapin and Philippe Meseure
Abstract: Animation of topological transformations, such as fractures, cracks, tears, crumbles or fragmentations, is a new challenge in Computer Graphics and Animation. We propose a new way to model and animate topological changes, allowing the programmer to design any type of topological changes and animation mapping. This model is based on organizing the complex modeling activity into three clearly defined simpler sub-activities: 1) point-based animation, which enables a wide variety of possible temporal phenomena; 2) topological-based modeling, which makes it possible to manage a wide variety of shape-independent topologies and topological transformations; 3) free, non predetermined, association between both, and 4) final output of an animated geometrical model exhibiting any complex behavior. We experimented the proposed method by modeling tearing effects on deformable garments, on rifts and crack effects on 3D objects, and finally by modeling imaginary and paradoxical topological transformations associated with realistic Physics-based animation. Besides improving the consistency and the robustness of the modeling process of such complex phenomena, our aim is also to offer a user-centered programming environment to the Computer Graphics and Animation programmers and designers, to enlarge their modeling and experimentation abilities, and to stimulate their creativity.
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Paper Nr: 43
Title:

Deformable Muscle Models for Motion Simulation
Authors:

Tomáš Janák and Josef Kohout
Abstract: This paper presents a methodology for interactive muscle simulation. The fibres of individual muscles are represented by particles connected by springs, thus creating a deformable model of the muscle. In order to be able to describe human musculoskeletal system, contact between pairs of muscles as well as muscles and bones must be accounted for. Therefore, collision detection and response mechanism which allows both types of contact (soft body vs. rigid body and soft vs. soft body) is presented. The solution is a part of a project dedicated to improvement of the effectiveness of osteoporosis prediction and treatment.
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Paper Nr: 65
Title:

Coupling Camera-tracked Humans with a Simulated Virtual Crowd
Authors:

Jorge Ivan Rivalcoba Rivas, Oriam De Gyves, Isaac Rudomín and Nuria Pelechano
Abstract: Our objective with this paper is to show how we can couple a group of real people and a simulated crowd of virtual humans. We attach group behaviors to the simulated humans to get a plausible reaction to real people. We use a two stage system: in the first stage, a group of people are segmented from a live video, then a human detector algorithm extracts the positions of the people in the video, which are finally used to feed the second stage, the simulation system. The positions obtained by this process allow the second module to render the real humans as avatars in the scene, while the behavior of additional virtual humans is determined by using a simulation based on a social forces model. Developing the method required three specific contributions: a GPU implementation of the codebook algorithm that includes an auxiliary codebook to improve the background subtraction against illumination changes; the use of semantic local binary patterns as a human descriptor; the parallelization of a social forces model, in which we solve a case of agents merging with each other. The experimental results show how a large virtual crowd reacts to over a dozen humans in a real environment.
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Short Papers
Paper Nr: 9
Title:

Action Graph - A Versatile Data Structure for Action Recognition
Authors:

Jan Baumann, Raoul Wessel, Björn Krüger and Andreas Weber
Abstract: This work presents a novel and generic data-driven method for recognizing human full body actions from live motion data originating from various sources. The method queries an annotated motion capture database for similar motion segments, capable to handle temporal deviations from the original motion. The approach is online-capable, works in realtime, requires virtually no preprocessing and is shown to work with a variety of feature sets extracted from input data including positional data, sparse accelerometer signals, skeletons extracted from depth sensors and even video data. Evaluation is done by comparing against a frame-based Support Vector Machine approach on a freely available motion capture database as well as a database containing Judo referee signal motions and concludes by demonstrating the applicability of the method in a vision-based scenario using video data.
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Paper Nr: 36
Title:

Simulation of Surgical Cutting in Deformable Bodies using a Game Engine
Authors:

Martin Kibsgaard, Kasper K. Thomsen and Martin Kraus
Abstract: Simulators as a training tool for surgeons are becoming more important with the increase of minimally invasive surgery and a wish to limit training on animals, especially in the field of robotic surgery. Accessibility to surgery simulators is currently limited and the ability to cut is restricted. This paper presents a feasibility study for implementing academic methods in a low-cost game engine. Expanding on previous work, a lowcost surgery simulator is implemented to adress these issues. We focus on the implementation of cutting in deformable objects in a game engine. The deformable objects are implemented using a spring mass model combined with a volumetric tetrahedral mesh. The cutting algorithm is semi-progressive and allows for arbitrary cuts in the deformable objects. The prototype was evaluated by a chief surgeon with expertise in robot surgery and experience with commercial simulators. The low-cost prototype presents a step towards robotic surgery simulators that are able to simulate complete surgical procedures.
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Paper Nr: 42
Title:

Virtual Characters with Affective Facial Behavior
Authors:

Ana Paula Cláudio, Augusta Gaspar, Eder Lopes and Maria Beatriz Carmo
Abstract: This paper describes an application that generates a simulation of a jury with one to three virtual humans capable of exhibiting facial and body expressions controllable in real-time. This control is performed through an interface that combines facial action elements (AU-Action Units, as described in the Facial Action Coding System), with upper-body postures. The level of detail of this control offers a range of possible combinations to obtain emotional expressions. Besides offering the possibility of controlling the postures of the virtual characters, the application allows the user to choose, among a pre-defined set, the virtual characters that compose the jury, and is able to introduce in the simulation some extra, potentially distractive or annoying events. We envisaged two contexts for using this application: i) assisting psychotherapists in exposure therapy of patients suffering from anxiety of public speaking, particularly in front of a jury in an assessment situation; ii) supporting nonverbal behaviour research carried out by psychologists. The development of the application has been closely monitored by a psychologist that is part of our team. This application is a low-cost approach, which uses only free software and models and resorts to common equipment; it is easy to install and use by people without expertise in informatics. So far, we have performed an evaluation with therapists in the first application context, obtaining encouraging results.
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Paper Nr: 78
Title:

A Pen and Paper Interface for Animation Creation
Authors:

P. Figueroa, J. Arcos, D. Rodriguez, J. Moreno and F. Samavati
Abstract: We present a Sketch Based Interface that allows non-expert users to create an animation with sound from a drawing on paper. Current animation programs may be daunting for novice users due to the complexity of their interfaces. In our work, users first draw a sketch on paper. Such a sketch is then processed by our tool and converted to an animation that includes sound. We do this process by means of a predefined set of 2D symbols and words that represent 3D characters, animations, and associated sounds. We present three studies of the proposed system, one related to the accuracy of the recognition process, another on the convenience of our system, and a third on the effect of sound on the final animation.
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Paper Nr: 35
Title:

Automatic Fly-through Camera Animations for 3D Architectural Repositories
Authors:

Patrick Knöbelreiter, René Berndt, Torsten Ullrich and Dieter W. Fellner
Abstract: Virtual fly-through animations through computer generated models are a strong tool to convey properties and the appearance of these models. In, e.g., architectural models the big advantage of such a fly-through animation is that it is possible to convey the structure of the model easily. However, the path generation is not always trivial, to get a good looking animation. The proposed approach in this paper can handle arbitrary 3D models and then extract a meaningful and good looking camera path. To visualize the path HTML/X3DOM is used and therefore it is possible to view the final result in a browser with X3DOM support.
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Paper Nr: 74
Title:

Retrieval, Recognition and Reconstruction of Quadruped Motions
Authors:

Björn Krüger, Hashim Yasin, Rebeka Zsoldos and Andreas Weber
Abstract: Different techniques have been developed for capturing and retrieval, action recognition and video based reconstruction of human motion data in the past years. In this paper, we focus on how these techniques can be adapted to handle quadruped motion capture data and which new applications may appear. We discuss some particularities that must be considered during large animal motion capture. For retrieval, we derive suitable feature sets from quadrupeds motion capture data to perform fast searches for similar motions. Based on the retrieval techniques, the action recognition can be performed on the input motion capture sequences as well as on input video streams. We further present a data-driven approach to reconstruct quadruped motions from video data.
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Area 4 - Interactive Environments

Full Papers
Paper Nr: 48
Title:

Perceptual Evaluation of Photo-realism in Real-time 3D Augmented Reality
Authors:

Mathias Borg, Martin M. Paprocki and Claus B. Madsen
Abstract: We present a framework for creating photo-realism of three-dimensional augmented objects, as well as a perceptual evaluating of the scenes. A setup utilizing different lighting conditions is created. Different parameters affecting the realism are evaluated. These are camera artefacts, shadows, number of lights for shading, highlights and geometry. The results show that silhouettes of the shadows and the geometry, and highlights on specular objects are important, as well as the simulation of noise, for creating a photo-realistic augmentation. Furthermore, a side by side comparison is conducted to verify that it is possible to render a virtual object in real-time, which is perceived as real under the best conditions.
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Paper Nr: 62
Title:

Symbol Adaptation Assessment in Outdoor Augmented Reality
Authors:

Maria Beatriz Carmo, Ana Paula Afonso, António Ferreira, Ana Paula Cláudio and Edgar Montez
Abstract: A challenge in presenting augmented reality information, particularly in outdoor environments, is to distinguish the virtual symbols from the background image. In this paper we report on a user study that leverages prior knowledge about adaptations to improve symbol conspicuity by expanding its application to outdoor environments and mobile handheld devices. We considered two types of adaptation that yielded good results indoors, namely adding a border around the symbol and adjusting the colour luminosity, and tested them outdoor in daylight. We also introduced partial and total adaptation modes that differed in the scope of the symbols to adapt: only the ones that are almost imperceptible from the background versus every symbol overlaying the real world image. Results from users’ questionnaires reveal that the border adaptation continues to be the favourite regardless of the outdoor lighting conditions, and yet we did not find differences in symbol detection performance in comparison with adjusting colour luminosity. The border adaptation was also considered the best to preserve symbol semantics when combined with the total adaptation mode, thus making it a versatile option for augmented reality applications.
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Paper Nr: 72
Title:

Sensing Immersive 360º Mobile Interactive Video
Authors:

João Ramalho and Teresa Chambel
Abstract: Video has the potential for a strong impact on viewers, their sense of presence and engagement, due to its immersive capacities. Multimedia sensing and the flexibility of mobility may be considered as options to further extend the video’s immersive capacities. Mobile devices are becoming ubiquitous and the range of sensors and actuators they incorporate is ever increasing, which creates the potential to capture and display 360º video and metadata and to support more powerful and immersive video user experiences. In this paper, we explore the immersion potential of mobile interactive video augmented with visual, auditory and tactile multisensing. User evaluation revealed advantages in using a multisensory approach to increase immersion and user satisfaction. Also, several properties and parameters that worked better in different conditions were identified, which may help to inform design of future mobile immersive video environments.
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Short Papers
Paper Nr: 11
Title:

Evaluating the Usability of Recent Consumer-grade 3D Input Devices
Authors:

C. Siegl, J. Süßmuth, F. Bauer and M. Stamminger
Abstract: Recently, 3D input devices such as the Microsoft Kinect sensor or the Leap Motion controller became increasingly popular - the later specialized in recognizing hand-gestures, advertising a very precise localization of tools and fingers. Such devices promise to enable a touchless interaction with the computer in three-dimensional space enabling the design of entirely new user interfaces for natural 3D-modeling. However, while implementing a modeling application we found that there are still fundamental problems that can not easily be solved: The lack of a precise and atomic gesture for enabling and disabling interaction (clicking gesture) and a poor human depth perception and localization within an invisible coordinate frame. In this paper, we show why the precision of the interaction is not limited by hardware but software constraints.
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Paper Nr: 45
Title:

Haptic Rendering using Support Plane Mappings
Authors:

Konstantinos Moustakas
Abstract: This paper presents a haptic rendering scheme based on distance maps over implicit surfaces. Using the successful concept of support planes and mappings, a support plane mapping formulation is used so as to generate a convex conservative representation and efficiently perform collision detection. The proposed scheme enables, under specific assumptions, the analytical reconstruction of the rigid 3D object’s surface, using the equations of the support planes and their respective distance map. As a direct consequence, the problem of calculating the force feedback can be analytically solved using only information about the 3D object’s spatial trasnformation and position of the haptic probe. Moreover, several haptic effects are derived by the proposed mesh-free haptic rendering formulation. Experimental evaluation and computational complexity analysis demonstrates that the proposed approach can reduce significantly the computational cost when compared to existing methods.
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Paper Nr: 67
Title:

Interactive Visualizer for the Extended Perspective System as Support for Architectural Design
Authors:

Robin Burgess, Teresa Chambel, Ana Paula Cláudio, Maria Beatriz Carmo, Carlos Albuquerque, José Vitor Correia, Luís Romão, Susana Rosado Ganhão, Manuel Couceiro da Costa, Ana Santos Guerreiro and Sara Garcia
Abstract: The flexibility of free-hand drawing perspectives denotes the dynamic nature of human sight and no single perspective system, linear or curvilinear, can translate human vision with such agility. For instance, linear perspective cannot deal with large fields of view, and curvilinear perspectives introduce curvature in lines. But together, complementing each other, they can overcome many of their limitations. This paper describes an interactive computational tool for architectural visualization – a digital perspectograph that implements a new theoretical and operative hybrid solution to perspective, the Extended Perspective System (EPS) – and presents a user evaluation carried out to determine its usability, perceived usefulness, satisfaction and ease of use, as an interactive tool to support the design process in architecture. It also aimed to learn about the most effective and appreciated features and interface design options to support the EPS perspective, and identify potential directions for improvement. The user study involved participants with different backgrounds – students and experts, in the target audience of architects and informatics engineers with experience in using and developing interactive tools, HCI and computer graphics. The visualizer was highly appreciated, in terms of layout, available features, produced images and flexibility, and the most effective design options were identified, mainly for their simplicity, visibility, and familiarity. It was considered advantageous compared to conventional perspective visualizers, and users would like to see it integrated into 3D modelling tools.
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Paper Nr: 71
Title:

A Video Browsing Interface for Collecting Sound Labels using Human Computation in SoundsLike
Authors:

Jorge M. A. Gomes, Teresa Chambel and Thibault Langlois
Abstract: Increasingly, movies and videos are becoming accessible as enormous collections over the Internet, and in social media, demanding for new and more powerful ways to search and browse them, based on video content analysis and classification techniques. The lack of large sets of labelled data is one of the major obstacles for the Machine-Learning techniques that are used to build the relevant models. This paper describes and evaluates SoundsLike, an interactive web application that adopts a Human Computation approach through a Game With A Purpose to engage users in movie soundtrack browsing and labelling, while maintaining or improving the entertaining quality of the user experience.
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Paper Nr: 1
Title:

Towards a Natural Interaction for Rapid Prototyping of Parametric Closets
Authors:

Iván Rodríguez, Celso Campos, Enrique Barreiro, Jorge Vázquez and Rocío Veiga
Abstract: Custom closets customers usually lack the expertise to design their desired closet. The use of a software tool that incorporates the design expertise might allow them to sketch their ideas without third party oversight. While architecture related applications are very powerful and make it possible to have an accurate graphical representation of real world, these Computer-Aided Design (CAD) tools demand high technical training and their use in the engineering field is generic. Our work, framed within the development of a rapid prototyping tool of custom closets called Sketch Arm, introduces an interaction proposal that seeks to minimize the time and complexity associated with typical operations in CAD. Supported by multi-touch capabilities of today’s mobile devices, our system allows users to manipulate the closet structure directly in real time by using a minimalist graphical user interface (GUI) together with a touch interface based on easily recognizable gesture patterns. Direct on-screen data manipulation is very attractive to the end-user in general and highly beneficial for novice IT users in particular while gesture-based interaction is extremely intuitive for performing artistic tasks. Throughout the article, we will describe in depth the designed interaction system and we will present the original solutions we made to common problems in touch systems like accuracy and occlusion.
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Paper Nr: 13
Title:

QR Codes on Curved Media Facades - Two Approaches for Inverse Distortion based on Raytracing and Image Warping
Authors:

Morin Ostkamp, Sven Luzar and Gernot Bauer
Abstract: Media facades and other public displays are a common sight in our everyday life. They can be found at various places, such as shopping malls or traffic hubs, e.g., the Times Square in New York City or Shibuya Crossing in Tokyo. Thanks to advances in technology, media facades are not bound to plane, rectangular shapes. Thus, many media facades are curved to increase their visual appearance or to better harmonize with the building behind. One example of such a curved media facade is the “Medienfassade” in the city of Münster. The shown content, however, is visually distorted due to the facade’s concave shape. That visual distortion may cause problems for certain types of content, i.e., QR codes, that may thus not be scanned with mobile apps. Since QR codes became popular in recent years, it appears desirable to display these codes on curved media facades, too. Thus, we propose two preprocessing approaches to compensate for the visual distortions of the curved media facade. An in-situ evaluation showed that both approaches can be used to “rectify” the distorted QR codes and let them be scanned successfully.
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Paper Nr: 15
Title:

Lazy Work Stealing for Continuous Hierarchy Traversal on Deformable Bodies
Authors:

Vinícius da Silva, Claudio Esperança and Ricardo Guerra Marroquim
Abstract: This study presents the results of research in dynamic load balancing for Continuous Collision Detection (CCD) using Bounding Volumes Hierarchies (BVHs) on Graphics Processing Units (GPUs). Hierarchy traversal is a challenging problem for GPU computing, since the work load of traversal has a very dynamic nature. Current research resulted in methods to dynamically balance load as the traversal is evaluated. Unfortunately, current grid-based GPU computing interfaces are not well suited for this type of computing and load balancing code can generate excessive overhead. This work presents a novel algorithm to address some of the most glaring problems. The algorithm uses the new concept of lazy work stealing, which tries to get the most out of the parallel capabilities of GPUs by greedy work stealing and lazy work evaluation. Also, the algorithm is designed to augment shared memory usage per block and diminish CPU-GPU context exchange penalties.
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Paper Nr: 24
Title:

SeGTE: A Serious Game to Train and Evaluate Basic Life Support
Authors:

Claudia Ribeiro, Joana Tiago, Micaela Monteiro and João Pereira
Abstract: Basic life support (BLS) is the level of medical care which is used for victims of life-threatening illnesses or injuries until they can be given full medical care at a hospital. It can be provided by trained medical personnel, including emergency medical technicians, paramedics, and by laypersons who have received BLS training. BLS is generally used in the pre-hospital setting, and can be provided without medical equipment. The ability to respond to an emergency situation can be the difference between life and death. Acknowledging this fact has made decision-makers, governments and Non Government Organizations (NGO) to make a priority to spread this knowledge and skills to the general population. Currently, BLS is taught in a standard course provided by the Red Course or certified entities, where the pedagogical content given to the students is a mix of theoretical and practical training where life-size mannequin are used. In this paper we argue that serious games could help spread this knowledge through the general population and it could also be used to refresh the knowledge of people that have been certified in BLS in the past. In order to test this hypothesis we have developed the SeGTE game and performed an evaluation of its effectiveness on conveying such pedagogical content.
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Paper Nr: 70
Title:

A Bare-Hand Gesture Interaction System for Virtual Environments
Authors:

Benjamín Hernández and Alejandro Flores
Abstract: Hand-based gestures provide direct mappings of user actions to 3D UI tasks; they are becoming a more attractive interaction alternative than keyboards, mice, controllers, among others. In this paper, we present a fast algorithm for hand gesture recognition for interaction in virtual environments. The method applies mathematical morphology operators (binarization and dilation) to acquire a clean segmented hand image from a depth data stream on which a curvature-metric and K-means algorithm is applied to detect the fingertips, then using fingertip and palm positions together with anthropomorphic metrics and a rule based system we perform gesture recognition. In addition, the intermittence gesture spotting problem is reduced using a digital integrator. Finally, a set of virtual environments were designed to demonstrate the performance, reliability and feasibility of our method.
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Area 5 - Social Agents in Computer Graphics

Short Papers
Paper Nr: 52
Title:

Domain Specific Sign Language Animation for Virtual Characters
Authors:

Marco Romeo, Alun Evans, Daniel Pacheco and Josep Blat
Abstract: This paper describes the design, implementation and results of a system to animate a virtual character to sign in International Sign (IS) By automatically parsing the input data, the system blends animations smoothly together in order to create a coherent and understandable presentation in sign language, with equal importance assigned to both hand and facial animation. Following the blending step, a video is rendered in a variety of formats suitable for distribution. The system was created in collaboration with groups of people with impaired hearing who were fluent in IS, and who were able to validate the results. We present a test case of the system in the shape of ‘Borja’, a virtual character who signed biweekly updates of the Barcelona World Race sailing regatta 2010/2011.
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